1. Field of the Invention
This invention relates to apparatus for stimulating plant growth under controlled conditions and, more particularly, to novel and highly-effective apparatus that is better adapted than prior apparatus to circulate air around the plants grown within the apparatus, to provide photostimulation of plants housed within the apparatus without enabling substantial escape of light from the interior of the apparatus, and to control and optimize the conditions of plant growth.
2. Description of the Prior Art
There is a great need for indoor laboratory apparatus capable of performing carefully controlled experiments relating to plant physiology and of maximizing the production of cultivated plants in a given period of time and utilizing a given amount of space. The great majority of cultivated plants are of course grown outdoors in a more-or-less natural setting in order to take advantage of sunlight, rain, soil and the vast amount of available space. However, the cultivation of plants in natural settings outdoors has certain drawbacks.
For one thing, it is not possible under such conditions to perform carefully controlled experiments to determine optimum levels of plant temperature, nutrition, watering and exposure to light or to determine whether genetic or environmental factors are responsible for certain observed differences among plants.
Moreover, rainfall is in general not adequately predictable and at different times may be too much or too little. Control of watering outdoors by means of irrigation degrades the soil over extended periods of time because of salt and other deposits left by evaporating water. Sunlight is more predictable than rainfall but is essentially uncontrollable. It varies with cloud cover (which is not adequately predictable or controllable) and with the season, latitude, and other factors. Soil quality can be analyzed and controlled to a degree with fertilizer but is always changing because of erosion, runoff from adjacent fields, depletion by plant uptake of nutrients, enrichment by plant decay, etc. Because of these problems, many scientific experiments of significant merit cannot be performed in a natural outdoor setting or even in an outdoor setting in which conditions are partially controlled through use of irrigation, fertilizer, etc.
In recognition of the problems attendant upon the cultivation of plants outdoors for scientific purposes and for the purpose of maximizing the production of plants per unit of space-time, minimizing the inter-nodal length between budding sites, and optimizing the "root to shoot to fruit ratio", significant efforts have been made for many years to develop indoor laboratory apparatus capable of performing carefully controlled experiments relating to plant physiology and of regulating and optimizing the conditions of plant growth.
It is believed that the most advanced, sophisticated and successful laboratory apparatus heretofore developed for this purpose is a device invented but not patented by the present applicant. The prior apparatus provides for controlling the lighting, watering, nutrition and temperature of plants grown therein. The lighting is provided by columnar (linear) fluorescent lamps ("stick lights") arranged around the interior perimeter of the housing with their respective longitudinal axes oriented vertically. The lighting is turned on and off in a regular cycle that provides photostimulation of the plants within the housing alternating with periods of relative darkness. Watering is done manually. Nutrition is tailored to the specific needs of the plants grown in the apparatus by analyzing the soil after a period of growth to determine which nutrients the plants have taken up and in what amounts. The nutrients required by the plants are thereafter supplied in the correct proportions at regular intervals. Temperature is controlled by keeping the apparatus indoors and by providing vents for the circulation of air through the apparatus.
However, the vents are formed and located with reference to the light sources and interior reflective surfaces of the housing so as to enable the passage of a substantial light flux from the interior to the exterior of the housing. This reduces the efficiency of the apparatus, since a certain percentage of the light generated makes no contribution to the stimulation of plant growth and is thus "wasted".
The requirements of temperature control by air circulation and maximum utilization of the light flux for photostimulation of the plants grown in the apparatus are to some extent contradictory. In order to provide adequate circulation of air, the vents must be of adequate size. Vents of adequate size for air circulation tend to enable the escape of a substantial flux of light from the apparatus, thereby reducing the efficiency of the light in stimulating plant growth.
It has been found moreover that the distribution of light from columnar lamps is not totally uniform and that the assembly of the device including, for example, six columnar lamps is more time-consuming than one would wish, particularly in a laboratory where many such devices are maintained.